1. Field of the Invention
The present invention relates to a packet transfer network using data selection switching based on a receiving comparison and a data packet transfer method.
2. Description of Related Art
In an internet, which is a typical example of the conventional data packet transfer system on a packet transfer network, a data packet received from a transmitting terminal is transmitted to one of possibly optimal transmission paths, which is selected on the basis of a destination address described in a header attached to the packet by a packet transfer node or a router. Packet transfer nodes in succeeding stages perform similar processing to transmit the data packet to a node or a host having a final destination address.
In the packet transfer node in which the data packet is processed, one packet received is merely transmitted to one path. Therefore, a data packet is neither copied nor forcibly abandoned as a whole packet transfer network and the data packet is basically transmitted from a transmitting node thereof to a receiving node uniformly.
That is, if a packet transfer node transfers a data packet correctly and reliably and there is no fault such as data loss in a transmission path thereof, the data packet can safely reach a destination node. However, if a packet is not transferred due to congestion of processing in or fault of a hardware of the packet transfer node or data loss in the transmission path, a destination node performs a recovery operation to receive the lost data packet by detecting the fault and requesting the transmitting side of a re-transmission of the data packet.
As shown in “Packet re-sending control system” disclosed in JP H01-269339A, each of nodes between a transmitting node and a receiving node performs a receiving confirmation for each data packet with adjacent nodes by using a system in which a packet re-transmission control is performed between adjacent transmitting node and receiving node.
However, there are problems in the above mentioned prior art technique, which will be described below.
A first one of the problems is that, although the cause of the phenomenon of the loss of data packet occurs in a relaying node or a transmission path, the loss of data packet can be detected in only a node in which data packet is assembled. That is, since it is usual that the assembling of data packet is performed in a last node, that is, the destination node, a loss of a data packet on the way to the destination node is determined in assembling some data packets.
A second problem is that, since the re-transmission request of data packet is made to a transmitting node, there is a time delay from a time at which data packet is lost until to a time at which a re-transmitted data packet is correctly received by a destination node. In order to detect a lost data packet without delay, it may be considered that a data packet is reconstructed in every packet transfer node. In such case, however, the merit of data packet transfer may be lost. Even in the technique disclosed in JP H01-269339A, there are problems that a delay occurs due to sacrifice of the merit of capability of transfer processing of every packet without consideration of inter-packet path, which is a feature of the packet transfer, by performing a receipt confirmation for every packet between adjacent nodes and that additional buffer resources are required.
The third problem is that, when a destination node is shifted in a packet transfer network, a delay occurs from a completion of a notice of a new location to which the destination is shifted until a data packet can be received by the new location. The reason for this is that, since, when the notice of the new location to which the destination node is to be shifted is made for the packet transfer nodes and the transmitting node, the data packet is not transferred to the new location unless a transfer path is changed, a delay occurs between a time at which the notice of the transfer path to the new location is received by a repeating nodes and the transmitting node and a time at which an information of the new transfer path to the new location is updated.